JP4569345B2 - Image forming apparatus and image forming method - Google Patents

Description

  The present invention relates to an image forming apparatus and an image forming method.

  In recent years, image forming apparatuses such as copiers, printers, facsimiles, and the like have been required to increase speed and improve image quality, and in order to meet these demands, image forming apparatuses employing a digital gradation reproduction method have been put into practical use. Yes. In the digital gradation reproduction method, an image is decomposed into pixels, data of each pixel is subjected to image processing by an image processing device, and then a recorded image composed of dots on a recording medium such as recording paper by an image output device. Form. In such an image output apparatus, a density gradation method and an area gradation method are widely known as methods for reproducing gradation information of an image.

  The density gradation method is a method having multi-value gradation reproducibility even when viewed at the microscopic pixel level of the image output apparatus, and is realized by, for example, a sublimation type thermal method. In addition, when properly managed, there is an advantage that it is easy to realize high image quality, but there is a problem that the characteristics of plain paper, high speed, stability, etc. are lacking. For this reason, the area gradation method is widely used for printers.

  The area gradation method is limited to the two states where ink is applied or not applied when viewed at the microscopic pixel level of the image output device, and the gradation is reproduced by converting the shade of the image to the size of the area. As one of them, there is a method in which each pixel of the input image is further decomposed into finer fine pixels, and the density of each pixel is associated with the area ratio of the fine pixel. A representative example of this method is a density pattern method.

Further, as an optical scanning method of the photosensitive member by the image writing unit (VCSEL ROS) of the surface emitting semiconductor laser, an adjacent exposure method in which a plurality of exposure beams (for example, 32) are all exposed in one scan, There is a double exposure method in which exposure is performed by scanning twice while shifting by half pitch (16 lines) (Patent Document 1).
JP 2003-255247 A

  However, in the double exposure method, if the exposure write position in the main scanning direction is shifted for some reason, the shifted scanning line has a problem that the exposure energy per unit area is reduced and white lines are formed.

  Factors that cause the scanning position shift include a shift in video data in the main scanning direction, a distortion for each surface of the polygon mirror, a variation in magnification due to vibration of the mirror in the ROS, and the like. The pixel position shift in the main scanning direction occurs due to distortion for each surface of the polygon mirror and magnification fluctuation due to vibration of the mirror in the ROS.

  As a countermeasure for the distortion of each surface of the polygon mirror, improvement of the polishing accuracy of the mirror can be considered, but there is a problem that the yield is lowered in the case of inspection, and the mirror becomes expensive to increase the yield. As a countermeasure against the magnification fluctuation due to the vibration of the mirror in the ROS, a ROS case itself having a high rigidity (for example, aluminum die cast) may be used, but the cost increases. In addition, although anti-vibration measures can be considered, the cost increases.

  Accordingly, the present invention has been made in view of the above problems, and provides an image forming apparatus and an image forming method capable of suppressing the occurrence of white streaks due to an exposure writing position shift in the main scanning direction with an inexpensive configuration. For the purpose.

In order to solve the above problems, the present invention is described in a page description language sent from the outside in an electrophotographic image forming apparatus that exposes a photosensitive member by scanning a plurality of exposure beams a plurality of times . A controller that interprets drawing data and performs color conversion and gradation correction on the output image data, and performs screen processing on the image data output from the controller according to the designated screen line number and growth pattern A printer engine control unit having a screen processing unit and a pulse generation unit that converts the image data processed by the screen processing unit into a pulse signal and outputs the pulse signal; and laser light generated according to the pulse signal output from the pulse generation unit. Exposure means for exposing and scanning the photosensitive member, and the screen processing unit has a predetermined screen. By changing the growth sequence, as one pixel isolated in the main scanning direction is not generated, and determining the screen shape. According to the present invention, the growth direction of the scan clean by the main scanning direction, even when the pixel offset in the main scanning direction occurs, it is possible to halt a minimum the influence of the deviation, the main as a result It is possible to suppress the occurrence of white streaks due to the exposure writing position shift in the scanning direction.

The screen processing unit is characterized in that a recording color with a lower brightness makes an obtuse angle with respect to the main scanning direction. Thereby, it is possible to suppress the occurrence of white streaks due to the exposure writing position shift in the main scanning direction . White muscle, so conspicuous as lightness low color (e.g., black), to set the screen angle as likely this phenomenon noticeable color obtuse.

The present invention interprets and outputs drawing data described in a page description language sent from the outside in an electrophotographic image forming method in which a photosensitive member is exposed by scanning a plurality of exposure beams a plurality of times. A control step for performing color conversion and gradation correction of the image data to be obtained, a screen processing step for performing screen processing on the image data output from the first step according to the designated screen line number and growth pattern, and A printer engine control step having a pulse generation step for converting and outputting the image data processed in the screen processing step to a pulse signal, and exposing and scanning the photosensitive member with a laser beam generated according to the pulse signal output from the pulse generation step. An exposure step, wherein the screen processing step comprises a preliminary step. The screen growth order determined is changed, and the screen shape is determined so that one isolated pixel does not occur in the main scanning direction . According to the present invention, the growth direction of the scan clean by the main scanning direction, a main scanning (FS: Fast Scan) even when the pixel offset in the direction occurs, the stave to a minimum the influence of the deviation As a result, it is possible to suppress the occurrence of white stripes due to the exposure writing position shift in the main scanning direction.

The screen processing step is characterized in that a recording color with a lower brightness makes an obtuse angle with respect to the main scanning direction.

  According to the present invention, it is possible to provide an image forming apparatus and an image forming method capable of suppressing the occurrence of white streaks due to the exposure writing position shift in the main scanning direction with an inexpensive configuration.

  Hereinafter, the best mode for carrying out the present invention will be described. FIG. 1 is a block diagram showing an embodiment of an image forming apparatus of the present invention. As shown in FIG. 1, the image forming apparatus 1 is an image forming apparatus that forms a latent image by scanning a plurality of light beams at the same position a plurality of times, and includes an image processing unit 2 and a marking engine 3. The image processing unit 2 includes a controller 21 and a printer engine control unit 22. The controller 21 includes a PDL interpretation unit 211, a drawing unit 212, and a rendering unit 213. This example shows a configuration in which an image is drawn according to drawing data described in PDL (page description language) sent from an external computer or the like, and the drawn image is formed on a sheet.

  Drawing data described in PDL from an external computer (PC) is input to the controller 21 via the interface unit. The controller 21 performs drawing in accordance with drawing data described in PDL sent directly from a computer or via a network or the like. The PDL interpretation unit 211 interprets drawing data described in PDL and controls operations according to various commands.

  The drawing unit 212 generates an intermediate code for drawing according to the interpretation of the drawing data by the PDL interpretation unit 211. The drawing unit 212 includes a color conversion unit, a TRC / γ correction unit, and the like. The color conversion unit converts a drawing color (for example, a color in the RGB color space) designated by the drawing data described in PDL into a color (for example, a color in the YMCK color space) used in the marking engine 3. This color conversion unit can be configured by, for example, a three-dimensional lookup table (hereinafter referred to as a DLUT), a matrix operation using a conversion matrix, or the like.

  The TRC / γ correction unit performs gradation correction processing for output to the marking engine 13 in accordance with a TRC (Tone Reproduction Curve) and a γ value. The TRC / γ correction unit can be configured by, for example, a one-dimensional lookup table (LUT). The rendering unit 213 renders the image data for one page suitable for the marking engine 3 based on the intermediate code generated by the drawing unit 212. Note that the image data is generated in accordance with the drawing resolution in the marking engine 3. When image data is sent from the outside, resolution conversion and the like are also performed by the rendering unit 213 or the drawing unit 212.

  The printer engine control unit 22 includes a screen processing unit 221 and a pulse generation unit 222. The printer engine control unit 22 converts the image data output from the decomposer into an electrical signal and outputs it so that the marking engine 3 can form an image. The screen processing unit 221 performs screen processing on the image data output from the controller 21 according to the designated screen line number and growth pattern. Note that the screen processing in the screen processing unit 221 may be performed by the drawing unit 212 by load distribution.

  The pulse generator 222 converts the image data screen-processed by the screen processor 221 into a pulse signal for driving the marking engine 3 and outputs the pulse signal. The printer engine control unit 22 has a configuration corresponding to the marking engine 3. The marking engine 3 forms an image on a sheet in accordance with a drive signal such as a pulse signal output from the printer engine control unit 22.

  FIG. 2 is a diagram illustrating a configuration example of the image forming unit. Here, the description will be made with the reflection mirror omitted. The individual light emitting points of the VCSEL light source group 380 constituting the semiconductor laser 38, that is, the plurality of laser beams L emitted from the VCSEL 380a are collimated (collimated) by the collimator lens 382 into laser beams having a predetermined beam diameter. This laser light is incident on the polygon mirror 39 via the cylindrical lens 387, and is reflected by its reflection surface (six surfaces in the figure) as the polygon mirror 39 rotates, and is deflected respectively.

  The laser beam L reflected and deflected by the polygon mirror 39 passes through a toroidal lens 388 having a tilt correction function and a scanning lens group 384 having an fθ function, and is a photosensitive drum 32 as an image carrier placed on the surface to be scanned. An image is formed on the spot 386 on the surface to be scanned. The reflection mirror 391 and the photodetector 392 are incident on the photodetector 392 at a position within the deflection range of the laser beam L and not involved in scanning of the surface to be scanned. Is arranged. In order to detect the laser beam L1 with the photodetector 392, the laser is turned on immediately before the laser beam L1 is deflected to the photodetector 392 during the scanning period, and is turned off before the scanning range necessary for the original scanning. Control is performed.

  The start of modulation of the laser light according to the image data is controlled by the main scanning synchronization signal output from the photodetector 392. As the VCSEL light source group 380, a VCSEL 380a serving as a light source is arranged on the surface of the semiconductor substrate 381 in a two-dimensional matrix, or a plurality of VCSELs 380a arranged in one line (in-line). This photosensitive member exposure unit (FIG. 2) is a main part in the marking engine of FIG. 1, and is combined with a developing device, a transfer device, and a fixing device (not shown) to form a desired image on recording paper. is there.

  3 to 6 are views for explaining a method of growing a screen according to an embodiment of the present invention. The screen processing unit 221 makes the growth direction of the screen less affected by the double exposure shift in the main scanning direction by giving a weight to the main scanning direction. 3 to 6, the screen processing unit 221 grows the screen in the order of (1) to (8). As indicated by reference numerals 101 and 102 in FIG. 3A, the screen processing unit 221 sets the minimum width of the screen shape in the main scanning direction to at least two pixels in the recording pixel unit, and sets the minimum pixel unit in the main scanning direction to two dots. That's it. As shown by reference numerals 201 and 202 in FIG. 3B, the screen processing unit 221 sets the minimum width of the screen shape in the main scanning direction to at least two pixels in the recording pixel unit.

  As shown in FIG. 3C, the screen processing unit 221 performs area modulation by giving priority to the main scanning direction (exposure scanning direction) as the growth direction of the screen. As shown in FIG. 3 (4), the screen processing unit 221 grows the sub-scanning direction by subtracting the pixels 401 to 404 in the main scanning direction indicated by dotted lines in the process of growing the screen. Thus, when growing in the sub-scanning direction, the main scanning direction is reduced so that the sub-scanning direction pixels are equal to or larger than the minimum unit. As shown in FIG. 5 (8), the screen processing unit 221 grows the sub-scanning direction by subtracting the pixels 801 to 804 in the main scanning direction indicated by dotted lines in the process of growing the screen.

  As shown in FIG. 6, the screen angle is obtuse with respect to the main scanning direction. That is, the screen angle is set to an acute angle (an angle closer to the main scanning direction) than 45 ° with respect to the process direction. By defining the minimum pixel unit in the main scanning direction and setting the growth direction of the screen as the main scanning direction, even if a pixel position shift in the main scanning direction occurs, the influence of the shift can be minimized. As a result, the occurrence of white stripes can be suppressed. Further, since the white streak is more conspicuous as the color is lighter (for example, black), it is preferable to set the screen angle to an obtuse angle for a color where this phenomenon is conspicuous. Therefore, it is preferable that the screen processing unit 221 makes the screen angle an obtuse angle with respect to the main scanning direction as the recording color has a lower brightness.

  FIG. 7 is a diagram for explaining the influence of pixel position deviation when priority is given to growth in the main scanning direction. The screen processing unit 221 does not cause white streaks even when pixel position shifts 901 to 904 are generated by performing area modulation with the growth direction of the screen giving priority to the main scanning direction.

  FIG. 8 is a diagram for explaining the influence of pixel position deviation (generation of white stripes) when priority is given to growth in the sub-scanning direction. Contrary to the above, the screen processing unit 221 has poor reproducibility of isolated pixels when pixel position shifts 911 to 914 occur when area modulation is performed with the screen growth direction giving priority to the sub-scanning direction. Therefore, it becomes a white line.

  FIG. 9 is a diagram for explaining the influence of pixel position deviation when the screen angle is 45 ° or more. In the case where the clean angle is 45 ° or more with respect to the main scanning direction, when pixel position deviations 921 to 923 occur, the reproducibility of isolated pixels deteriorates, resulting in white streaks.

  FIG. 10 is a diagram for explaining the influence of the image position shift when the screen angle is 45 ° or more in a line type screen. In the case where the clean angle is 45 ° or more with respect to the main scanning direction, if the pixel position deviations 931 to 936 occur, the reproducibility of isolated pixels deteriorates, resulting in white streaks.

  FIG. 11 is a diagram for explaining the influence of pixel position deviation when the screen angle is 45 ° or less. As shown in FIG. 11, by making the screen angle an obtuse angle with respect to the main scanning direction, that is, by making the screen angle more acute than 45 ° (an angle closer to the main scanning direction) with respect to the process direction. Even if pixel position deviations 941 to 944 occur, white stripes do not occur.

  FIG. 12 is a diagram for explaining an example of a screen angle of 45 ° or less. As shown in FIG. 12, by making the screen angle an obtuse angle with respect to the main scanning direction, that is, by making the screen angle more acute than 45 ° (an angle closer to the main scanning direction) with respect to the process direction. Even if the pixel position deviations 951 and 952 occur, white stripes do not occur.

  13 to 15 are diagrams for explaining screen growth. In this example, a 4 × 4 threshold table is used as the screen matrix. A combination of the four matrices will be described as one gradation reproduction matrix. In FIG. 13, reference symbol A indicates a 4 × 4 threshold table, and reference symbol B indicates a threshold table in which four 4 × 4 threshold tables are combined. (A) is a conventional threshold value table, (b) is a threshold value table used in the present invention, (c) is a diagram showing a state of screen growth, and (d) is a shape change so as not to generate one isolated pixel during the screen growth process. FIG.

FIG. 14 is an operation flowchart. When 8 × 8 image data is input in step S11, the screen processing unit 221 performs screen processing using an 8 × 8 threshold table in step S12. In step S13, when the pixel density (gradation) is 3 gradations, the screen processing unit 221 converts the screen density to a screen pattern corresponding to the gradation (3) in FIG. 13 in step S14. In step S15, when the pixel density (gradation) is 7 gradations, the screen processing unit 221 converts to a screen pattern corresponding to the gradation (7) in FIG. 13 in step S16. Finally, 8 × 8 data is output. As shown in FIG. 15, the screen processing unit 221 circulates the flowchart of FIG. 14 and performs screen processing on the entire image area.

  Returning to FIG. 13 again, the screen processing unit 221 grows the screen in the order of gradation 1 to gradation 13 in FIG. As shown in gradation 1 in FIG. 8C, the screen processing unit 221 sets the minimum width of the screen shape in the main scanning direction to at least two pixels in the recording pixel unit so that no isolated pixel is generated in the main scanning direction. To do. As indicated by reference numeral 3A1 of gradation 3 in FIG. 5C, since one isolated pixel in the main scanning direction is generated, the screen processing unit 221 changes the screen shape based on the pixel determination, and As shown in reference numeral 3A2 of gradation 3 in FIG. 4D, one isolated pixel is prevented from occurring in the main scanning direction. Similarly, as indicated by reference numeral 7A1 of gradation 7 in FIG. 7C, one isolated pixel is generated in the main scanning direction. Therefore, the screen processing unit 221 uses the reference numeral 7A2 based on the pixel determination. As shown in FIG. 4, it is ensured that no isolated pixel is generated. In this example, the screen shape is changed at gradations 3, 7, and 13. As described above, it is possible to suppress the occurrence of white streaks due to the exposure writing position shift in the main scanning direction with an inexpensive configuration.

  Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications, within the scope of the gist of the present invention described in the claims, It can be changed.

1 is a block diagram showing an embodiment of an image forming apparatus of the present invention. It is a figure which shows one structural example of an image formation part. It is a figure for demonstrating the growth method of the screen by the Example of this invention. It is a figure for demonstrating the growth method of the screen by the Example of this invention. It is a figure for demonstrating the growth method of the screen by the Example of this invention. It is a figure for demonstrating the growth method of the screen by the Example of this invention. It is a figure for demonstrating the influence of the pixel position shift at the time of main scanning direction growth priority. It is a figure for demonstrating the influence (white stripe generation | occurrence | production) of the pixel position shift at the time of subscanning direction growth priority. It is a figure for demonstrating the influence of a pixel position shift when a screen angle is 45 degrees or more. It is a figure for demonstrating the influence of the image position shift when a screen angle is 45 degrees or more with a line type screen. It is a figure for demonstrating the influence of pixel position shift when the clean angle is 45 degrees or less. It is a figure for demonstrating the example of the screen angle of 45 degrees or less. It is a figure for demonstrating screen growth. It is a flowchart of a screen growth process. It is a figure for demonstrating a screen processing order.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Image processing part 3 Marking engine 21 Controller 211 PDL interpretation part 212 Drawing part 213 Rendering part 22 Printer engine control part 221 Screen processing part 222 Pulse generator

Claims (4)

In an electrophotographic image forming apparatus that exposes and scans a photoconductor so that each pixel is exposed at least twice using a plurality of exposure beams.
A controller that interprets drawing data described in a page description language sent from outside, and performs color conversion and gradation correction of output image data;
A screen processing unit that performs screen processing on the image data output from the controller according to a specified screen line number and growth pattern, and a pulse that converts the image data processed by the screen processing unit into a pulse signal and outputs the pulse signal A printer engine control means having a generator;
Exposure means for exposing and scanning the photosensitive member with a laser beam generated in accordance with a pulse signal output from the pulse generation unit,
The image processing apparatus, wherein the screen processing unit determines a screen shape by changing a predetermined growth order of screens so that one isolated pixel does not occur in the main scanning direction . The image forming apparatus according to claim 1, wherein the screen processing unit makes an obtuse angle with respect to a main scanning direction for a recording color with a low brightness . In an electrophotographic image forming method in which a photosensitive member is exposed and scanned so that each pixel is exposed at least twice using a plurality of exposure beams.
A control step for interpreting drawing data described in a page description language sent from the outside and executing color conversion and gradation correction of output image data;
A screen processing step for performing screen processing on the image data output from the first step according to a designated screen line number and growth pattern, and converting the image data processed in the screen processing step into a pulse signal and outputting the pulse signal A printer engine control step having a pulse generation step of:
An exposure step of exposing and scanning the photosensitive member with a laser beam generated according to the pulse signal output from the pulse generation step,
In the image processing method, the screen processing step determines a screen shape so as not to generate one isolated pixel in the main scanning direction by changing a predetermined growth order of the screens . 4. The image forming method according to claim 3 , wherein in the screen processing step, the screen angle is set to be obtuse with respect to the main scanning direction as the recording color has a lower brightness .

Images